A switching mode power supply (SMPS) is widely used for converting an input voltage into an output voltage by controlling the switching action of at least one switch. Constant ON time (COT) control is typically used for controlling a SMPS for its quick transient response. In a SMPS with COT control, a switch is turned on once a predetermined condition is detected, for example, when detecting that a feedback signal indicative of the output voltage drops below a reference signal. Then the switch is maintained in the ON state for a constant ON time. And at the end of the ON time, the switch is turned off.
When the ON time is fixed, it would cause large variation in switching frequency which varies with the variation in the input voltage and the output voltage of the SMPS. And large variation in switching frequency would introduce interference to the rest of the system. And also, the switching frequency is required to be limited in order to minimize the switching loss.
Accordingly, an improved COT SMPS is required to at least address one or some of the above deficiencies.